Exponentially Modified Gaussian functions—A good model for chromatographic peaks in isocratic HPLC?

Summary The Exponentially Modified Gaussian (EMG) function is fitted to a variety of typical peaks from isocratic HPLC, to assess its validity for peak characterization. This model has previously been applied, but with simplifying assumptions, allowing estimation of peak parameters from simple front and rear half-width measurements. The full EMG function is employed in this work. The results of the simplified approach have been compared to the EMG fitted results. Comparison is also made to fitted Gaussian functions. Results show that the EMG function is a good model for typical LC peaks, under a range of conditions, and that the simplified approaches give close correlation for a range of peak assymetries.     

Geometry of simple molecules. 2. Modeling the geometry of AX3E and AX2E2 molecules through the nonbonded interaction (NBI) model

A new conceptual model of molecular geometry is presented, called the nonbonded interaction (NBI) model. This model is applied to the geometries of the AX3E and AX2E2 (A = N, O, P, S, As, Se, or Te; X = H, F, Cl, Br, I, CH(3), tBu, CF3, SiH3, Sn(tBu)3, or SnPh3) molecule types. For these molecules, the NBI model can be quantified on the basis of a balance between terminal atom-terminal atom (X-X) interactions and lone pair-terminal atom (E-X) interactions. The empirically observed X-A-X angles range from 91.0 degrees (SeH2) to 180 degrees (O(Sn(tBu)3)2), and the NBI model predicts the X-A-X angle with a mean unsigned error of 1.0 degrees using the empirical A-X distance, 1.5 degrees using the LMP2/6-31G** A-X distance, and 1.1 degrees using the MMFF94 A-X distance. This level of precision compares well to the LMP2/6-31G**-predicted X-A-X angles and is significantly better than the MMFF94-predicted X-A-X angles. Terminal groups that are not sufficiently spherical (CF3, SiH3, and SnPh3) can still be addressed qualitatively by the NBI model, as can molecules with a mixture of terminal groups. The NBI model is able to explain, often quantitatively, the geometry of all of the molecules studied, without any additional postulates or extensive parametrization.     

Sodium pyridine‐3‐carboxyl­ate

The title compound, also known as sodium nicotinate, Na⁺·C₆H₄NO₂⁻, consists of two unique Na atoms coordinated to two unique pyridine‐3‐­carboxyl­ate ligands through the N atoms and carboxylate groups. One Na atom and one pyridine‐3‐­carboxyl­ate ligand lie on a twofold axis. Extensive Na coordination results in a three‐dimensional array comprising infinite NaO₂CR chains linked by intrachain Na—N bonds.     

Understanding how the herpes thymidine kinase orchestrates optimal sugar and nucleobase conformations to accommodate its substrate at the active site: a chemical approach

The herpes virus thymidine kinase (HSV-tk) is a critical enzyme for the activation of anti-HSV nucleosides. However, a successful therapeutic outcome depends not only on the activity of this enzyme but also on the ability of the compound(s) to interact effectively with cellular kinases and with the target viral or cellular DNA polymerases. Herein, we describe the synthesis and study of two nucleoside analogues built on a conformationally locked bicyclo[3.1.0]hexane template designed to investigate the conformational preferences of HSV-tk for the 2'-deoxyribose ring. Intimately associated with the conformation of the 2'-deoxyribose ring is the value of the C-N torsion angle chi, which positions the nucleobase into two different domains (syn or anti). The often-conflicting sugar and nucleobase conformational parameters were studied using North and South methanocarbadeoxythymidine analogues (6 and 7), which forced HSV-tk to make a clear choice in the conformation of the substrate. The results provide new insights into the mechanism of action of this enzyme, which cannot be gleaned from a static X-ray crystal structure.     

Synthesis and characterisation of molecularly imprinted catalytic microgels for carbonate hydrolysis

Novel molecularly imprinted microgels incorporating arginine and tyrosine side chains as functional monomers have been designed and synthesised with percentages of cross-linker ranging from 70 to 90%. Full chemico-physical characterisation including M_r, coil density and size particle determination concluded that all polymer preparations obtained can be classified as microgels. Molecular imprinting using a phosphate template was used to generate catalytic microgels for the hydrolysis of p-nitrophenyl carbonates. Kinetic characterisation of the catalytic activity of the different preparations indicated that values of critical monomer concentration (C_M) and percentage of cross-linker play an important role in determining the catalytic efficiency of the different preparations. Microgels containing 70% cross-linker were the only ones following the Michaelis-Menten saturation model and kinetic parameters were obtained using 4 mg/ml of M397: V_max = 1.34 × 10⁻⁶ M s⁻¹ (S.E. 1.28 × 10⁻⁷) and K_M = 2.38 × 10⁻³ M (S.E. 3.1 × 10⁻⁴).     

Arylsulfonate-based nucleophile assisting leaving groups

[Chemical reaction: See text] The synthesis and unique reactivity of a series of arylsulfonate-based nucleophile assisting leaving groups (NALG) containing oligomeric ether units (including crown ethers) attached to the arylsulfonyl ring in the ortho orientation are described. The reactions of a variety of these ether-containing alkyl sulfonates with metal halides proceeded at substantially greater rates than electronically similar sulfonates. These ether-containing leaving groups also displayed marked selectivity for lithium halides relative to the corresponding sodium and potassium salts in nucleophilic displacement reactions.     

Synthesis and structural characterization of the first quaternary plutonium thiophosphates: K(3)Pu(PS(4))(2) and APuP(2)S(7) (A = K, Rb, Cs)

The first quaternary plutonium metal thiophosphates have been synthesized by the reactive flux method and characterized by single-crystal X-ray diffraction: K(3)Pu(PS(4))(2) (I), KPuP(2)S(7) (II), RbPuP(2)S(7) (III), and CsPuP(2)S(7) (IV). All four compounds crystallize in the monoclinic space group P2(1)/c with Z = 4. Compound I has cell parameters of a = 9.157(1) A, b = 16.866(2) A, c = 9.538(1), and beta = 90.610(3)degrees. Compound II has cell parameters of a = 9.641(1) A, b = 12.255(1) A, c = 9.015(1) A, and beta = 90.218(1)degrees. Compound III has cell parameters of a = 9.8011(6) A, b = 12.3977(7) A, c = 9.0263(5) A, and beta = 90.564(1)degrees. Compound IV has cell parameters of a = 10.1034(7) A, b = 12.5412(9) A, c = 9.0306(6) A, and beta = 91.007(1)degrees. Compound I is isostructural to a family of rare-earth metal thiophosphates and comprises bicapped trigonal prismatic PuS(8) polyhedra linked in chains through edge-sharing interactions and through thiophosphate tetrahedra. Compounds II-IV crystallize in a known structure type not related to any previously observed actinide thiophosphates and contain the (P(2)S(7))(4-) corner-shared bitetrahedral ligand as a structural building block. A summary of important bond distances and angles for these new plutonium thiophosphate materials is compared to the limited literature on plutonium solid-state compounds. Diffuse reflectance spectra confirm the Pu(III) oxidation state and Raman spectroscopy confirms the tetrahedral PS(4)(3-) building block in all structures.     

Cell-wall engineering of living bacteria

The cell walls of living bacteria were chemically modified by adding cell-wall precursors. As the precursors to be incorporated into the cell wall, UDP-MurNAc pentapeptide, lipid I, and lipid II derivatives were synthesized. The aimed compounds were attached to the amine residue of lysine at the pentapeptide moiety. Fluorescein-attached UDP-MurNAc pentapeptide was efficiently incorporated into both Gram-positive and Gram-negative bacteria. In the case of Gram-negative bacteria, such as Escherichia coli, the permeability of the outer membrane (lipopolysaccharide layer) was enhanced by EDTA treatment before the incorporation. For Gram-positive bacteria, UDP-MurNAc derivatives were incorporated in the cell wall without EDTA treatment due to the lack of the lipopolysaccharide layer. Furthermore, instead of dyes, a ketone group was attached to the UDP-MurNAc pentapeptide. The ketone group was also delivered to the bacterial cell wall of lactic acid bacteria, giving a platform to attach large molecules on the surface.     

Oxidative dissolution of copper and zinc metal in carbon dioxide with tert-butyl peracetate and a beta-diketone chelating agent

A series of beta-diketone ligands, R(1)COCH(2)COR(2) [tmhdH (R(1) = R(2) = C(CH(3))(3)); tfacH (R(1) = CF(3); R(2) = CH(3)); hfacH (R(1) = R(2) = CF(3))], in combination with tert-butyl peracetate (t-BuPA), have been investigated as etchant solutions for dissolution of copper metal into carbon dioxide solvent. Copper removal in CO(2) increases in the order tfacH < tmhdH < hfacH. A study of the reactions of the hfacH/t-BuPA etchant solution with metallic copper and zinc was conducted in three solvents: scCO(2) (supercrical CO(2)); hexanes; CD(2)Cl(2). The etchant solution/metallic zinc reaction produced a diamagnetic Zn(II) complex, which allowed NMR identification of the t-BuPA decomposition products as tert-butyl alcohol and acetic acid. Gravimetric analysis of the amount of zinc consumed, together with NMR studies, confirmed the 1:1:2 Zn:t-BuPA:hfacH reaction stoichiometry, showing t-BuPA to be an overall two-electron oxidant for Zn(0). The metal-containing products of the copper and zinc reactions were characterized by elemental analysis, IR spectroscopy, and, as appropriate, NMR spectroscopy and single-crystal X-ray diffraction [trans-M(hfac)(2)(H(2)O)(CH(3)CO(2)H) (1, M = Cu; 2, M = Zn)]. On the basis of the experimental results, a working model of the oxidative dissolution reaction is proposed, which delineates the key chemical variables in the etching reaction. These t-BuPA/hfacH etchant solutions may find application in a CO(2)-based chemical mechanical planarization (CMP) process.     

N‐(2‐Amino­benz­yl)‐N,N‐bis­(quinolin‐2‐ylmeth­yl)amine

The title new diquinaldine derivative, C₂₇H₂₄N₄, forms mol­ecular assemblies organized by inter­molecular quinoline π–π stacking [3.356 (3) and 3.440 (3) Å] and both inter‐ and intra­molecular N—H⋯N hydrogen bonds [3.039 (3)–3.104 (3) Å and 129 (2)–172 (2)°]. The combination of such inter­actions provides readily definable contacts that propagate along each crystallographic axis.